We will study elements of the cellular and humoral immune responses in HLA-A2+ patients with breast and ovarian cancer whose tumors are HER2 positive. Patients will receive intradermal vaccination with autologous monocytes which have been made to express HER2-derived peptide by in vitro incubation with the peptide. Following vaccination they will have sampling of peripheral blood, vaccination site, saline control vaccination site, and metastatic tumor site (if accessible). Cell-mediated anti-tumor activity induced by vaccination will be studied as cells isolated from these sites are assayed in vitro for ability to lyse HER2 positive cell lines in the absence (specific cytotoxicity) or presence (antibody-dependent cytotoxicity) of in vitro anti-HER2 antibody. Humoral antitumor response before and after vaccination will be studied by assaying serum for the amount of circulating endogenous anti-HER2 antibody.